Available channels

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Every MTA channel has a unique name containing up to 32 characters. Only lowercase letters, numbers, underscores, and dollar signs should be used in channel names.

Certain channel names are reserved for particular uses. Moreover, the MTA (especially the Job Controller) recognizes certain families of channel names, (channel name prefixes), and will make internal assumptions about such channels. There are both hard-coded expectations of certain special channel name usage, plus in particular some historical but now wide-spread "conventions" regarding use of certain tcp_* channel names. Using channel names in a conflicting manner can lead to serious problems. MTA administrators are encouraged to use these channels for the stated purposes and in general to pick channel names of their own that do not conflict with these usage conventions.

Modern reserved channel names
Name Reserved For
bitbucket Bit bucket channel (deletes all messages queued to it)
bsin_* BSMTP inbound channels
bsout_* BSMTP outbound channels
circuitcheck Message circuit checking channel
conversion Message body part conversion channel
defragment Message defragmentation channel
filter_discard Channel for delayed deletion of message discarded or jettisoned due to Sieve actions (or analogous *_ACCESS mapping table flag effects)
hold Channel where messages are temporarily detained for administrative purposes such as user migration
ims-ms Channel delivering to the Message Store (without use of LMTP; see also the tcp_lmtpss channel when LMTP is used instead).
ims-ms_* Additional channels delivering to the Message Store.
l The local channel; in modern Messaging Server configurations, a "placeholder" channel that performs no delivery but rather performs alias processing only.
native Delivery to UNIX /var/mail mailboxes.
pipe Pipe channel
pipe_* Additional pipe channels
process Processing channel
process_* Additional processing channels
reprocess Reprocessing channel
reprocess_ Additional reprocessing channels
sms* SMS channels
tcp_auth By convention, the SMTP-over-TCP/IP channel handling incoming authenticated messages.
tcp_intranet By convention, the SMTP-over-TCP/IP channel communicating with other internal hosts.
tcp_lmtpcs* By convention, LMTP client channels.
tcp_lmtpss By convention, the LMTP server delivering to the Message Store on an LMTP back end system.
tcp_local By convention, the SMTP-over-TCP/IP channel communicating with the Internet.
tcp_submit By convention, the SMTP SUBMIT server channel.
tcp_tas By convention, the SMTP-over-TCP/IP channel receiving telephony messages that need so-called "Guaranteed Message Deposit" (quota bypass for message delivery).
tcp_* Additional TCP/IP SMTP (or LMTP) channels
test_smtp_* Test (sample code) channels
uucp_ UUCP channel (UNIX, or DEC/Shell UUCP)

In addition to the above modern channel names, there are various obsolete or historical channels where use of those old channel names may cause confusion:

Outdated reserved channel names
Name or prefix Reserved For
address Extract addressing information from the body of a message
address_* Additional addressing channels
aoce_ Apple AOCE channels
bit_ Jnet (BITNET)
bull_ BULLETIN channels
cc_ cc:Mail channels
cn_ Internal usage by the national Australian network
ctcp_ Carnegie Mellon University TCP/IP channels; obsolete
d The DECnet MAIL channel; used to deliver messages across DECnet via VMS MAIL
d_ Additional MAIL-11 over DECnet channels
data_to_bitmap Raw FAX data to bitmap channel
data_to_bitmap_ Additional data to bitmap channels
directory Directory alias expansion channel
directory_ Directory alias expansion channels
dn_ PhoneNet over DECnet
dsmtp_ SMTP over DECnet
era_ ERA channels
etcp_ Excelan TCP/IP channels; obsolete
faxsr_ Fax Sr. channels
fax_to_data Inbound FAX to raw data channel
fax_to_data_ Inbound FAX to raw data channel
ff_ Microsoft® Mail channels
ftcp_ Network Research Corporation FUSION TCP/IP channels; obsolete
g3_to_fax Group 3 to FAX modem spooler
g3_to_fax_ Group 3 to FAX modem channels
ker_ Kermit protocol
ln_ Lotus Notes channels
mail_ General VMS MAIL delivery
mailserv Mail and list server channel
mhs_ Novell MHS channels
mime_to_x400 MIME to X.400 conversion channel
mime_to_x400_ MIME to X.400 conversion channels
mime_to_x40084_ MIME to X.400-1984 conversion channels; obsolete
mint MINT user agent from Wesleyan University
mr_ PMDF-MR gateway
mrif_ PMDF-MR as Message Router TS replacement channels
msgstore PMDF Message Store delivery channel
msgstore_ PMDF MessageStore channel
mtcp_ Process Software MultiNet (formerly Cisco MultiNet, formerly TGV MultiNet) TCP/IP channels; obsolete
netdata_ Netdata (PROFS) channels
notes_ VAX NOTES channels
osfl_ UNIX local channels
ovvm_ OV/VM (PROFS) channels
p Generic PhoneNet channel; used to communicate with a central PhoneNet host
p_ PhoneNet channels
pager E-mail to pager channel
pager_ Pager channels
popstore PMDF popstore delivery channel; a msgstore channel can be---and typically is -- used instead
profs_ PROFS channels
printer e-mail to spooled printer
printer_* Additional e-mail to spooled printer channels
ps_to_g3 PostScript to Group 3 FAX interpreter
ps_to_g3_ PostScript to Group 3 FAX channels
ptcp_ Process Software TCPware
px25_ PhoneNet over X.25; obsolete
qm_ QuickMail channels
snads_ SNADS channels
subject Channel to extract information from Subject: lines
sync_db_ Database synchronization channels
sync_dirbot_ Directory synchronization robot (DIRBOT) channels
sync_ldap_ LDAP directory synchronization channels
sync_ldif_ LDIF directory agent channels
sync_ln_ Lotus Notes directory agent channels
text_to_ps Text to PostScript converter
text_to_ps_ Additional text to PostScript channels
utcp_ ULTRIX (UCX) Connection TCP/IP channels; obsolete
vn_ UUCP channel (DECUS UUCP)
wpo_ GroupWise (WordPerfect Office) channels
wtcp_ Wollongong TCP/IP (WIN/TCP) channels; obsolete
x400_ X.400 channels
x40084_ X.400-1984 channels; obsolete
x400_to_mime X.400 to MIME conversion channel
x400_local X.400 transport channel
xapi_ MAILbus 400 channels
xsmtp_ SMTP over X.25; obsolete

See also: